It's the town or city that does the disposal whether that's burying, recycling, dumping at sea, or whatever. Again, this article isn't about whether we should produce plastic but how we should dispose of it once its collected.
The bag doesn't magically get from the store to the waste stream it has to be properly disposed of by the customer to make it there.
> once its collected
Its not the employees of the town or city ensuring that bag ever makes it to the employees of the town or city though, that's my point. Its the user of the plastic bag is where a lot of the breakdown in the chain happens. Its the fact you buy anything and the shop gives you a plastic bag to deal with. Which, a ton of people don't do a good job dealing with them! Similarly, they don't do a good job with drink containers and other packaging either.
Its not like its the city employees putting all the plastic bags in the creeks and the rivers and the fields and the woods. At least, not usually, and not normally in their course of duty.